In recent years, the electronic technique called as the “spintronics” has attracted a lot of attentions. Conventional electronics has utilized only the “electric charge” which is one of the characteristics of the electron. In the spintronics, in addition to the electric charge, the “spin”, which is another characteristic of the electron, is positively utilized. Specifically, the “spin current”, which is a flow of the spin angular momentum of the electron, is an important concept. Since the energy dissipation of the spin current is small, there is a possibility of achieving an information transmission in high efficiency by utilizing the spin current. Therefore, the generation, detection, and control of the spin current are important themes.
For example, a phenomenon is known, in which a spin current is generated when an electric current flows. This is called as the “spin-Hall effect”. Further, as an inverse phenomenon, it is known that an electromotive force is generated when a spin current flows. This is called as the “inverse spin-Hall effect”. The spin current can be detected by utilizing the inverse spin-Hall effect. Note that, both of the spin-Hall effect and the inverse spin-Hall effect are relevantly developed in materials having large “spin orbit coupling” (e.g., Pt, Au).
Further, according to recent researches, the existence of the “spin-Seebeck effect” in magnetic bodies has become clear. The spin-Seebeck effect is a phenomenon in which a spin current is induced in the direction parallel to the temperature gradient when the temperature gradient is applied to the magnetic body (for example, refer to the patent literature 1, the non-patent literature 1, and the non-patent literature 2). Namely, due to the spin-Seebeck effect, the heat is converted into the spin current (heat-spin current conversion). In patent literature 1, the spin-Seebeck effect in an NiFe film being a ferromagnetic metal is reported. In non-patent literatures 1 and 2, the spin-Seebeck effect on the interface between the magnetic insulating body such as yttrium iron garnet (YIG, Y3Fe5O12) and a metallic film is reported.
Note that, the spin current induced by the temperature gradient can be converted into the electric field (electric current, electric voltage) by utilizing the above-mentioned inverse spin-Hall effect. Namely, the “thermoelectric conversion” can be achieved in which the temperature gradient is converted into the electricity by utilizing both of the spin-Seebeck effect and the inverse spin-Hall effect.
FIG. 1 shows the structure of the thermoelectric conversion element disclosed in the patent literature 1. A heat-spin current conversion part 102 is formed on a sapphire substrate 101. The heat-spin current conversion part 102 has a laminated structure of a Ta film 103, a PdPtMn film 104, and an NiFe film 105. The NiFe film 105 has a magnetization of an in-plane direction. Further, a Pt electrode 106 is formed on the NiFe film 105, and the both edges of the Pt electrode 106 are connected to the terminals 107-1 and 107-2, respectively.
In the thermoelectric conversion element configured as said above, the NiFe film 105 has a function to generate a spin current from the temperature gradient due to the spin-Seebeck effect, and the Pt electrode 106 has a function to generate an electromotive force from the spin current due to the inverse spin-Hall effect. Specifically, when a temperature gradient is applied to the NiFe film 105 in an in-plane direction, a spin current is generated in the direction parallel to the temperature gradient due to the spin-Seebeck effect. Then, the spin current flows in from the NiFe film 105 to the Pt electrode 106, or flows out from the Pt electrode 106 to the NiFe film 105. In the Pt electrode 106, an electromotive force is generated in the direction orthogonal to the spin current and the NiFe magnetization direction due to the inverse spin-Hall effect. The electromotive force can be extracted from the terminals 107-1 and 107-2 formed on both edges of the Pt electrode 106.
As other related techniques, in patent literature 2, a spintronics device is disclosed, in which a spin wave spin current—pure spin current conversion is performed on the interface between a magnetic dielectric layer and a metal electrode. In patent literature 3, a microwave oscillation element which excites a microwave oscillation by injecting a pure spin current from a metal layer to a ferromagnetic layer is disclosed.